Prosthetic appliance



W. L. FITCH PROSTHETIC APPLIANCE Jan. 9, 1951 2 Sheets-Sheet 1 FiledJune 1'7, 1946 INVENTOR. WILL/AM L. FITCH ATTORNEY Jan. 9, 1951 w. L.FITCH 2,537,402

PROSTHETIC APPLIANCE Filed June 17, 1946 2 Sheets-Sheet 2 IN VEN TOR.

WILLIAM L. FITCH ATTORNEY Patented Jan. 9, 1951 UNITED STATES PATENTOFFIQE Fitch and Signs, Inc a corporation of Galiiornia Application June17, 1946, Serial No. 677,265

. G r ie???- fl his invention relates to prosthetic appliances and moreparticularly to an artificial armior use .case of an abovethe-yelbowamputation.

Prior art artificialarms usually failed to constitute a satisfactorysubstitute for the natural arm in two main respects. From a mechanicalviewpoint, inslrfiicienti torque was available to rotate the forearmabout the velbow to provide adequate facilities for lifting. From acosmetic viewpoint, the vpriorflart arms failed to simulate the swingingmovement of natural arm during walking, and from both a mechanical and acosmetic viewpoint the prior art arms failed to providecontinuouslifting movement and usually would have to/be locked in the carryingposition.

v. Olojects of the invention are, therefor,e, toproyideflan artificialarm which will simulate as closelyas possible the actiori of the naturalarm, which will be of simple-anddurabl'e construction, will beconvenient to wear and easy to operate.

In accomplishing these and other objects of the present invention, Ihave provided improved detailsofstructure, the preferred form of whichis illustrated in the accompanying drawings, wi r Eig, 1 isa generallylateral elevational view of il rt fiqia arm mb dyin the tu e of thepresent invention with the harness attached and the forearm partiallyflexed;

F -121 a n r l y an er e et n i of thearm with harness attached, theforearm semewh extr idedian r fin hook Omitted;

Fi -v1 i a enl r e i smfin a ro -S tipn alrview talgenalong alongitudinal mid-plane w s-r a d 11i g.'.4 is a view sirnilar toFig. 3,of a modification of the presentfinvention including a detacha, e lbpwiinte, .--5 his a fragmentary cross-sectional view similar to thatrofFig. 3 showing a non-spherical modificationiof the elbow joint;

Eight is a. generally anterior elevational view of themodificationof'Fig.5 with the forearm ex.-

Fig. 7 is a fragmentary view similar to that of Fig. 3;partially incross-section, showing a modificationjofttheielbow joint with the fiexorand extensor cables in. difierentplanes; and

Fig. 8 is a fragmentary cross-sectional view similarto that of Fig. 3showing a solid modificationof theforearm elbow member withlost-motionconnections for the. operating cables.

Rein-wring. more particularly to the drawing:

Numeral l indicates generally the upper arm member of he pr stlie iwhich ia tre b t r by sewing at 4 andZor by riveting as'fatlf l to ibalkae d'ek if v i e l i arm member l6 mayalsobe made offwotfiiipla i0fllat ene na keewe anre 2 bodylof the amputee by ,a harness generallyin-' dicated by the'numeral 21 The harness cons" s ofa rather wide bandvor trap 3 adapted tend over the shoulder of the amputated rm. Thisstrap is generally made of leaf her bfu lniay be of any other suitablematerial. Attached end portions of the strap 5 is a conn ngstrab 6adapted to extend hleneaththe' armpit "of the amputatedarm. Abelt'lfofleatheir or 1? br' adapted t'oextend beneath the ripper pc theother arm, passingrover the-back of a putee and around his chest to bucl fle'a-s at .8' o the stra 3. The'lbelt 3' is'ifa' s'ten'edibyfllseother convenient nieans'as at', 9 to the pos nor portion of the strap3'. flfhis'harness .diifersfiom the conventional harness particularly inthat t dispenses wi'th'fnumerons sue rem t "y st p5 and bucklesusuallyfouiidmthe p The ap erarm' member Fihtbludeis a'lower p91?- tionl9, shown in-Fig. 3 as made of wood. ,It may; howeaer'fhe' madeoifplasticQlaminatec'i fab tal, such as aluminum,-to provide 'a'ligstruction'; so 'long as ltliefrnatrial'is lof su'ifi strength.The'lovver'lportion ll'lilis 101 0? a as at ,i I to forn areceptacleioreferablyfline' leather .12 to receive the awaenagn the tuIfheioute'r se rate. of th portion ID is a layer [3' of pliablemateri ,p

r masaeuyisrh ana 5 constituting the $9 a et ifabe% la dl et ili e ofrelbowo int v A forearm {Sis shown of asubstantiallymni-r tarystructure, p reierlablyialiim' be either sand cast, die cast hr s' atthelproximal end thereof a por in the ram of "a sphere, consti orlaminated .falaric orthe like :and th b ,11 poiaonma be solid'inste'adofihollow as o A conventional amer eek {wr fattached tor he distal endof the forearm frhember 6 Tandi's' op erated by means .ofa 'lcable lfc Useparate harness (not' shown) in a convent; mamifl s w. c e

.To facilitate complete flexion without interference between the"anterior surfaces ot '1 the arm and the forearm, said 'surfa 3 and 2|,respectively. The forearm is pivoted to the upper arm at the elbow jointby means of a bolt or pin 22 passing through a lateral-medial diametralopening in the spherical portion [1 and fixed at its ends to supportingstraps 23, preferabl of metal, attached, as by screws 24, to the lateraland medial surfaces of the upper arm. To limit extension of the forearmto simulate the limitation of movement of a natural arm, a shoulder orstep 25 i formed on the forearm adjacent the elbow to abut acorresponding shoulder or step 26 formed on the upper arm (Fig. 3).

In the movement of a natural arm from the anatomical position hanging atthe side to the carrying position, the forearm is flexed simultaneouslywith the movement of the upper arm. As the upper arm is moved from aposition hanging at the side to the carrying position, the distancebetween a point on the body adjacent the spine of the scapula and apoint on the proximal portion of the posterior of the upper arm isincreased. Use is made of this increase in distance to actuate amechanism to flex the forearm.

A flexible cable 21, preferably of stranded steel but conceivably offiber, gut, Or the like, is attached to the forearm by means of a lostmotion connection adjacent the intersection of the spherical surface ofthe elbow ball I1 with the forearm proper. This connection includes anopening 28 through which the cable 21 passes into the hollow portion 29of the forearm member. Adjacent the end of the cable lying within theportion 29 a bead 30, larger than the diameter of the opening 28, isfixed. When tension is applied to the cable 21, the bead 30 engages theperiphery of the opening 28 and, thus, the tension on the cable istransmitted to the forearm in order to flex the latter. The opening v28is preferably located in a longitudinal anterior-posterior mid-plane ofthe forearm.

The cable 21 lies on the anterior surface of the spher l1 and enters theupper arm through an entrance opening 3! which is provided therein. Thecable then extends in a generally supralateral direction either througha bore 32 out directly through the material ill or, if more convenient,along a path substantially between the cover l3 and the material I0,merging superficially through an exit opening 33 on the lateral aspectof the upper arm.

The cable 21 is surrounded by a flexible sheath 34, of knownconstruction, made in the general form of a closely wound incompressiblehelix. The sheath 34 is anchored to the bucket by means of a loop 35 ofleather, fabric or metal, fastened to the bucket at a point superior ofthe opening 33, and two internally threaded beads 36 abutting the loopon either side. The beads can be fixed at any desired point on thesheath, in a known manner, by virtue of the difference in pitch betweenthe helix of the sheath, when compressed, and the internal threads onthe beads. The proximal end of the sheath terminates at the point 31.The upper end of the cable 21 is anchored by any convenient means, suchas a link 38 fastened to the harness strap 3 approximately adjacent thespine of the scapula of the amputee.

As the stump is raised toward the carrying position, the distancebetween the end of the cable attached to the anchor 38 and thetermination 31 of the sheath increases. That is, the sheath 34 is drawndownwardly over the cable 21. In other words, the cable 21 is drawnupwardl relative to and through the sheath 34. From another point ofview it may be said that as the upper arm is of the forearm H6.

flexed the cable 21 is pulled through the sheath 34 by the anchor 38.This action causes the bead 30 on the lower end of the cable 21 toengage the forearm beneath the opening 28 and thus flex or raise theforearm to carrying position. The cable 21 may hence be designated as afiexor cable. The opening 3! in the upper arm is so located as to liewithin the same equatorial plane of the ball or spher 11 as the opening28 in the forearm, whereby, during the aforedescribed movement of thecable 21, said cable lies along the circumference of a great. circle ofthe sphere l1 and, thus, has no tendency to veer on this path. Since thecable acts always at the circumference of a circle of the sphere lyingin a plane normal to the elbow axis and described about the elbow axisas acenter, th torque exerted by it on the forearm is always applied atthesame torque arm distance equal to the radiusfof the circle of thesphere. Assuming substantially constant tension on the cable 21 duringthe jlifting of the arm, this means that the torque acting on theforearm is also substantially constant. "In the embodiment illustrated,where the circle is a great circle of the sphere, the constant torquearm is the radius of the great circle, which is the radius of thesphere, and the torque acting on the forearm is the product of theradius of the sphere and the tension in the cable. This torqueiSfObviousl constant, if the tension in the cable is assumed to beconstant.

Under certain circumstances it may be desirable to provide a torque armof a length which varies during the flexion of the forearm. This may beaccomplished by substituting for the circle of the sphere an arcuatesurface, not circular about but generally concave about the' elbow axis,having any desired curvature or shape such as an involute, evolute,cycloid, etc. The torque arm will be the perpendicular distance betweenthe elbow axis and the line of action of the cable 21 as it leaves thearcuate surface, usually as a tangent. An example of such avariable-torque-arm construction is shown in Figs. 5 and 6 whereelements corresponding to those in Fig. 3 are generally indicated bynumerals greater by Ifiii than the corresponding numerals in Fig. 3. Theupper arm Nil is provided with a generally spherical concavity H5described about the axis of the elbow pivot pin 122 with a radiusslightly greater than the longest radius vector of the nonsphericalelbow ball"! l1 The flexor cable I21 and the extensor cable i39 areattached to the forearm HG through a lost-motion connection with beadsI30 and MI, respectively. In the position shown in Fig. 5, with theangle between the forearm and upper arm being about the cable I21 isacting at approximately a maximum torque arm, i. e. the length of theperpendicular from the axis of pin 122 to the line of action of thecable I21 is a maximum. Assuming that the force exerted on the cable i21is substantially constant throughout the flexion and extension range ofthe upper arm, this arrangement would be advantageous in that it appliesthe maximum lifting torque to the forearm under the conditions when thetorque exerted by the weight of the load on the hook or hand is amaximum. Since the cables l21 and I39 arenot traveling on geodesics ofthe nonspherical ball H1, it is, of course, necessary to provide a guidemeans to prevent shifting of the cable such as groove I60 shownespecially in Fig. 6 where cable I21 is broken away to better illustrateit.

ris etv oustnat any matron of the upper arm which increases the distancebetween the point gramme link 38 will cause flexing of the forearm,Because of this, the prosthesis simulates the behavior of a natural limbwhere the forecan be flexed when the upper arm is either flexed orabducted or both ilexe'd and abducted from the anatomical position. (ITo provide for extension of forearm an extensor cable 3d, similar tocable 2?, is used. The dam end of cable 3Q enters the hollow sphere ,I lthrough an opening on the posterior aspect thereof. The end is providedwith a bead ll, "sim'ilar' to bead 33. The connection of the cable 39 tothe sphere i! has the same lost motion properties as the connection ofcable 2'2. lhe cable 39 passes over the posterior surface of the s here17, enters the upper arm at an opening Q2 fon the posterior aspectthereof, and continues through a bore 43 which extends supra-medially"either through the material it or slightly be heath the leathercovering IS, in a manner complementary to that of bore 32. The cableemerges superficially through an opening 35 on the medial surface of thesupra-medially having its proximal end at ancliore'd to a -nk 33,similar to link 33, which is fastene'dto the harness 3 at a pointadjacent the anterior of the shoulder of the amputated ic'hored to thearm at by means similar to loop;35 'and beads 36.

it is apparent that when the upper arm is extended, the distanc eincreases between a point, such as i-ilfonthe anterior surface of theupper arm "and a point, such as 35, cnthe harness. Usejis nia'de of thisproperty of the geometry of the "arm't'o actuate the extensor cable 39.By vn' tue of "the arrangement of parts, the cable Isconstrained tofollow a-particularpath determined "by the following elements: the cableanchor 45, the sheath anchor '23, "the course of the'sh'eath thenpeningt2, the curvature of the sphere ii, the opening ti], and the bead ti.Two segments of this path are variable in length: (1;) the segmentbetween cable anchor 48 and sheathan c hor tag-meme by extension orflexion of the upper arm and (2) the segment between the opening 2 andopening ll variable by extension or flexion of the forearm. Since thesheath -47, as constructed and mounted, is

substantially invariable in length, the remaining segments of the pathof the cable are also invariable in length. tensible, any increase inlength of segment (1), tsiicha t .cau sdh e sion f the i arm must beaccompanied by a corresponding de crease in the length of segment (2).This decrease can be accomplished only by pivoting of the forearm aboutthe elbow axis in such a Way that the pening ii! approaches the opening32 and this pivoting is precisely the flexion of the forearm desired tosimulate mechanically and cosmetically the action of a natural arm.

The extensor cable 39 is illustrated as lying on the circumference ofthe same great circle of the sphere I? as the flexor cable 2?. Forproper coaction of the two cables, this implies that the increase indistance between anchor 36 and termination point 3? during flexion ofthe upper arm, say from anatomical position to carrying position, isequal to the increase in distance between sheath anchor 38 and cableanchor 4? when the upper arm is extended from carrying bucket id andcontinues 1 ja The cable 39 is surrounded by a flexible sheath 5?,similar to sheath 3%, which is an- Since the cable is inexposition toanatomical position. In the event that this latter increase is ei-racerthan the former, as is frequently the case on various amputees, thisdifference in increase 'is compensated for by causing the extensor cable39 to travel not on a great circle path but on a small circle path ofthe sphere If. The small circle chosen is of appropriate diameter toprovide the desired difference in cable travel over that of the greatcircle course for the same angular rotation of the forearm. Toaccommodate the new position of the cable, the openings 49 and 2 2 wouldbe shifted from the midplane of the arm although they would preferablyremain in a commonplane normal to the elbow axis. Since a cablefollowing a small circle course will tend to assume a greatcirclecourse, which is the shortest distance between two points o a sphere,this tendency must be overcome by providing a circumferential groovealong the chosensmall circle in the surface of the sphere -11 in whichthe cable 3;! will ride.

A modification showing the small-circle c'o'hstruction is illustrated inFig. 7 wherethe spherrcal lbow forearm member 21? is provided with theflexor cabl 227 traveling on the great-circle To use the-prosthesis-ofthe present invention, the bucket M is placed over the stump of an-annputated arm and the harness 2 is buckled in place on the amputee. Thecables 2'! and -39, in addition to moving-the forearm, serve to hold theprosthesis to the amputee, thus eliminating the need for numerous strapsfound in prior -,art prostheses. As thestump and upper arm of theprosthesis are raised, for example, flexed toward carrying position, thecable 2?, acting through thebead 3i! bearing against theedge of opening28, flexes the forearm. During this flexion of the forearm the edge ofthe opening 40 bears against the bead ll and thus draws the cable 39through the sheath 4?. This motion of cable 39 is facilitated by thedecrease in distancebetween the sheath anchor 43 and the cableanchor 4Bconsequent upon the flexing of theupper arm toward carrying position.

To extend the arm, as from carrying'position toward anatomical position,the stump anolupper arm member 1 of the-prosthesis are extended,increasing the distance between the sheath anchor 48 and cable anchor 46tending to draw the bead 4i againstthe edge of theopening iii and thusextend the forearm. This extension of the forearm causes the edge ofopening 28 to engage the bead 3i] and draw the cable 2'! downwardrelative to the sheath 34. This relative motion is facilitated by thedecrease in distance between the termination 3? of the sheath 34 and thecable anchor 38 consequent upon the extension of the upper arm.

In the event that the forearm is flexed without raising the upper arm,as for example, if the forearm strikes an object while swingingbackward, the bead 3i tends to remain in its position while the forearm.fiexes away from it. If the bead 39 were anchored to the forearm at theopening 28 this motion would tend to compress and kink the cable 21'.However, the forearm being hollow, the bead 30 and cable 27 merely feedinto the hollow space 29 and. the cable 21 is not 7 kinked. A Similaraction occurs, upon occasion, with the lost motion connection betwee theextensor cable 39 and the forearm. In the event that the sphere H ismade as a solid member, openings are provided in it to perform the lostmotion function of the hollow space 29.

Fig. 8 illustrates a modification having a solid elbow ball 35?. Thecable 321 with its bead 338 and the cable 339 with its bead 341 arelinked to the forearm with lost motion provided by the openings 36E and362, respectively. These can be made conveniently by drilling holesthrough the forearm with a conventional tapered-point drill taking carethat the proximal ends of the holes, such as 363, are large enough toallow the cables to pass through but small enough to restrain the.beads. The distal ends of the holes may be plugged as at 364.

Although the particular modification of the invention illustrated inFig. 1 shows the socket member of the elbow joint integral with theportion ll] of the upper arm and shows the ball member ll integral withthe forearm l5, nevertheless the elbow joint is readily adapted formanufacture as a separate unit easily installed in existing prior artarms. Such a unit is illustrated in Fig. 4 wherein the socket memberElla is made as a separate piece joined, as by a plurality of screws 49,to the lower end Illb of the conventional bucket member. Openings 56' inthe member Hla are provided for a screw driver to reach the screws 42.Similarly, the ball member lid is made as a separate piece adapted to befastened, as by screws 5 l, with a lap joint to a conventional prior areforearm ifia. This type of construction offers the additional advantageof adjustability. Frequently, a bucket after use beyond the fittingperiod will adapt itself to the wearer by rotating about thelongitudinal axis of the stump to a final permanent location differentfrom its position when originally fitted. This causes undesirablepronation or supination of the upper arm, forearms and hand. With theelbow joint made as a detachable unit, this rotation is easilycompensated for by merely unscrewing .the socket member a from thebucket, turning it, with the forearm attached, sufficiently tocounteract the rotation of the bucket and screwing it back onto thebucket at the new position.

While I have shown but certain embodiments of my invention, it issusceptible to further modification without departing from the spirit ofthe invention, I do not wish therefore, to be limited by the disclosuresset forth, but only by the scope of the appended claims.

I claim:

1. In a prosthesis for an arm amputated above the elbow having aharness, an upper arm memher including a bucket, and a forearm member, aball and socket elbow joint including a generally spherical socketportion at the distal end of said upper arm member, a generallyspherical ball portion on the proximal end of said forearm memberpivoted about the elbow axis to said upper arm member and in engagementwith the socket of said socket portion, said upper arm member having abore therethrough extending generally supra-laterally from an entranceopening on the anterior aspect thereof adjacent the intersection of ananterior-posterior longitudinal mid-plane with the anterior surface ofsaid socket to an exit opening on the lateral aspect of said upper armmember, a flexible cable sheath lying in said bore and emerging fromsaid exit opening and anchored to said upper arm member at a pointsuperior of said exit opening, a flexible cable having a lost motionconnection at its distal end with said ball portion and passing over theanterior surface of said ball portion along a great circle ath definedby said mid-plane and passing through said sheath, and means anchoringthe proximal end of said cable to said harness at a point adjacent thespine of the scapula of the amputated arm.

2. A prosthetic appliance for an arm having a ball and socket elbowjoint comprising an upper arm member having a socket formed therein, asubstantially hollow forearm member including a ball pivoted to saidupper arm member about the elbow axis and engaging said socket, anopening into said forearm member, a substantially inextensible cablehaving an end extending through said opening into said forearm member,means on said end of said cable to prevent withdrawal of said endthrough said opening, means on said upper arm guiding said cablegenerally superiorly relative to said upper arm, said cable passing overthe surface of said ball on a circle thereof lyilng in a plane normal tosaid elbow axis, and means to anchor said cable adjacent the shoulder ofsaid arm.

WILLIAM L. FITCH.

REFERENCES QITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,278,106 Caron Sept. 10, 19181,334,834 Blatchford Mar. 23, 1920 FOREIGN PATENTS Number Country Date326,422 Germany Sept. 28, 1920

